1. Field of the Invention
Aspects of the present invention relate to an electrode assembly for a lithium ion secondary battery and a lithium ion secondary battery using the same, and more particularly, to an electrode assembly for a lithium ion secondary battery in which a sealing tape attached to the outer circumference of an electrode assembly is formed of a material that has an affinity for an electrolyte and that absorbs the electrolyte to swell, or the external surface or the internal surface of the sealing tape is coated with the material so that the coating of the sealing tape swells when the electrode assembly is impregnated with the electrolyte, so that the electrode assembly is closely attached to a can, preventing the welding part of an electrode tab from being short circuited by the rotation or the floating of the electrode assembly and a lithium ion secondary battery using the same. A coated sealing tape of which the coating has a high affinity for an electrolyte and that absorbs the electrolyte to swell and a lithium ion secondary battery using the same are provided.
2. Description of the Related Art
In general, as portable wireless apparatuses, such as video cameras, mobile telephones, and portable computers, are lightweight and require sufficient energy sources, much research is dedicated to the secondary batteries used as the driving power sources of such apparatuses. The secondary batteries include an Ni—Cd battery, an Ni-MH battery, an Ni—Zn battery, and an Li-ion secondary battery. Among the above batteries, the Li-ion secondary battery is rechargeable and small, has a large capacity, and high operation voltage and energy density per unit weight. Thus, the Li-ion secondary battery is widely used in the portable electronic apparatus field.
FIG. 1 is an exploded perspective view of a common cylinder-type lithium ion secondary battery. A cylinder-type lithium ion secondary battery is herein described.
Referring to FIG. 1, a cylinder-type lithium ion secondary battery 100 includes an electrode assembly 110, a cylinder-type can 130 for accommodating the electrode assembly 110, an electrolyte, an insulating gasket 160, and a cap assembly 150 assembled with the upper part of the cylinder-type can 130 to seal the cylinder-type can 130 and to allow the flow of the current generated by the electrode assembly 110 to an external apparatus.
In the electrode assembly 110, a positive electrode plate 112 obtained by coating the surface of a positive electrode collector with a positive electrode coating portion, a negative electrode plate 114 obtained by coating the surface of a negative electrode collector with a negative electrode coating portion, and a separator 113 positioned between the positive electrode plate 112 and the negative electrode plate 114 to electrically insulate the positive electrode plate 112 and the negative electrode plate 114 from each other are wound to form a jelly-roll-like structure. Although not shown in the drawing, the positive electrode plate 112 can include the positive electrode collector formed of a thin metal plate having excellent conductivity, for example, an aluminum (Al) foil. The positive electrode plate 112 can also include the positive electrode coating portion, which coats the both surfaces of the positive electrode collector. A portion of the positive electrode collector without the positive electrode coating, that is, having a positive electrode non-coating portion, can be formed on both ends of the positive electrode plate 112. A positive electrode tab 116 that is formed of aluminum (Al) protrudes above the electrode assembly 110 and can be connected to the one end of the positive electrode non-coating portion.
Also, the negative electrode plate 114 comprises a negative electrode collector formed of a conductive thin metal plate, for example, a copper (Cu) or nickel (Ni) foil. And, the negative electrode plate 114 can include the negative electrode coating portion, which coats both surfaces of the negative electrode collector. A portion of the negative electrode collector without the negative electrode coating, that is, having a negative electrode non-coating portion, can be formed on both ends of the negative electrode plate 114. A negative electrode tab 118 that is formed of nickel (Ni) and protrudes downward from the electrode assembly 110 can be connected to the one end of the negative electrode non-coating portion. Insulating plates (not shown) for preventing the electrode assembly 110 from being connected to the cap assembly 150 and the cylinder-type can 130 can be further provided about the electrode assembly 110. A sealing tape 120 for supporting, protecting, and insulating the electrode assembly 110 is wound around the outer circumference of the electrode assembly 110. The sealing tape 120 is commonly formed of a polyolefin based material such as polyethylene (PE), polypropylene (PP), and polyimide (PI).
The cylinder-type can 130 includes a cylinder-type side plate 132 having a predetermined internal diameter. The internal diameter of the cylinder-type side plate 132 determines the size of the space within which the cylinder-type electrode assembly 110 is accommodated. The cylinder-type can 130 further comprises a bottom plate 134 to seal the lower part of the cylinder-type side plate 132. The upper part of the cylinder-type side plate 132 can be opened so that the electrode assembly 110 may be inserted. The negative electrode tab 118 of the electrode assembly 110 can be connected to the center of the bottom plate 134 of the cylinder-type can 130 so that the cylinder-type can 130 can function as the negative electrode. Also, the cylinder-type can 130 is commonly formed of nickel (Ni), steel (Fe), or an alloy of the above metals. A crimping unit 138 may be formed in the cylinder-type can 130 to couple the upper end of the cylinder-type can 130 to the cap assembly 150. A beading unit 136 is formed inwardly recessed in the cylinder-type can 130 to press the lower part of the cap assembly 150, and the beading unit 136 is formed a distance corresponding to the thickness of the cap assembly 150 below the crimping unit 138 .
The cap assembly 150 can include a safety vent 152, a current intercepting unit 154, a secondary protective element 156, and a cap-up 158. A protrusion that extends downward can be formed in the center of the safety vent 152. The protrusion is positioned in the lower part of the cap assembly 150 and may be transformed upward by the pressure generated in the secondary battery. A positive electrode tab 116 is withdrawn from one electrode plate between the positive electrode plate 112 and the negative electrode plate 114 of the electrode assembly 110; for example, the positive electrode plate 112 is welded to the predetermined position of the bottom of the safety vent 152 so that the safety vent 152 and the positive electrode plate 112 of the electrode assembly 110 are electrically connected to each other. A negative electrode tab 118 is withdrawn from one electrode plate between the positive electrode plate 112 and the negative electrode plate 114; so, the negative electrode plate 114 is electrically connected to the cylinder-type can 130 by the negative electrode tab 118. The connection of the negative electrode plate 114 and the negative electrode tab 118 can be electrical, direct, or any other connection to transfer current and electrons. The safety vent 152, the current intercepting unit 154, and the secondary protective element 156 prevent explosion of the secondary battery 100 by failing and releasing pressure. The safety vent 152 is transformed or broken when the pressure in the cylinder-type can 130 increases too much and damages the current intercepting unit 154. Also, the current intercepting unit 154 is damaged when the safety vent 152 is transformed to intercept current. The secondary protective element 156 intercepts current when the current in the current intercepting unit 154 exceeds a predetermined current the. Furthermore, a conductive cap-up 158 is provided to supply a positive electrode voltage or a negative electrode voltage to the outside is further positioned on the secondary protective element 156.
The insulating gasket 160 surrounds lateral portions of the safety vent 152, the current intercepting unit 154, the secondary protective element 156, and the cap-up 158 from the cylindrical-type can 130 as the cylindrical-type can 130 acts as the negative electrode.
Generally, the electrode assembly 110 easily floats and rotates in the cylinder-type can 130. As the electrode assembly 110 floats and rotates, so do the positive and negative electrode tabs 116 and 118, respectively. When an external shock, such as falling, is inflicted upon the cylinder-type lithium ion secondary battery, the welding part between the positive electrode tab 116 and the safety vent 152 and the welding part between the negative electrode tab 118 and the cylinder-type can 130 are damaged so that the internal circuit of the battery becomes disconnected. There is little change in the case of a polygon-type lithium ion secondary battery. The electrode assembly also floats and rotates such that the welding part of an electrode tab is damaged resulting in the internal circuitry of the battery becoming disconnected.